run the hackmii installer you used to install the homebrew channel and install bootmii (if you can as boot2, otherwise install it as a ISO). now go to the homebrew channel and press the home button on your wiimote and select Bootmii. Now using the power and reset buttons on your wii (power button to go left and reset to select), go to the icon that has the SD card on it and press reset. Then go to the icon that has the green icon going to the SD card and press reset. now you should be able to backup your nand